SALEM — Environmental advocates are looking to the quietest victims to point out natural gas leaks: trees.

The Salem Alliance for the Environment (SAFE), Salem Sound Coastwatch and city officials are working to find natural gas leaks as the city undergoes a wide-reaching street tree inventory.

There were more than 60 such natural gas leaks in Salem at the beginning of the year, while 99 had been plugged in 2016, according to maps available on HEETMA.org.

“SAFE heard about these gas leaks,” said Pat Gozemba, a co-chairperson of SAFE. “We got concerned initially because we realize that the kinds of gains that Massachusetts was making in terms of renewable energy — or the establishment of more and more renewable energy, which thus cut down on greenhouse gas emissions — was being offset by all the methane gas that was leaking from the aging infrastructure.”

Utility companies have been chasing small leaks in their networks of pipes for years now, as the ingredients in the gas has led to more leaks, Gozemba said.

Decades ago, pipes were put together with jute used to seal connections at joints.

“That was at a time when the natural gas that was coming through the pipeline had a lot more water in it,” Gozemba said.

But as the water content dropped, Gozemba said the jute used in the joints contracted. The result was several slow leaks.

These leaks aren’t necessarily dangerous. They aren’t detectable without a meter measuring the content of methane in the air. SAFE member Dave Rowand said it typically takes an unexplained dead tree to signal where there may be a leak.

Using trees as gas leak indicators isn’t new.

“As part of the training in the gas company, when they send crews out to look for the gas leaks, that’s one of the things they’re told — look for dead or dying trees,” Gozemba said. “That’s an indicator that there could be a gas leak there.”

The reason why? Trees need oxygen to grow.

“Gas percolates up through the soil and can drive out the oxygen, which is necessary for trees to survive,” Rowand said. “Any tree we see that’s distressed, dead or dying, there’s a possibility there’s a gas leak in the vicinity.”

What’s new about this process, however, is the volunteer effort to find leaks that utility companies might have missed. Any number of factors could conceal a small leak. Wind could dissipate leaking methane, for example.

“The hope with the information is that we can give more data to the gas company so they can be more aggressive about fixing these leaks, particularly leaks that are affecting these trees — which are, after all, the lungs of the Earth,” Gozemba said. “We’ll be able to share it with National Grid, and hopefully it’ll get National Grid to repair them.”

Ward 7 Councilor Steve Dibble, who represents southeast Salem, has been a vocal advocate for the trees and what methane, which is an ingredient in natural gas, in can do to them.

“On Buchanan Road, a bunch of neighbors have complained about the quality of the trees — trees dying,” Dibble said, “and two of the neighbors linked it to gas leaks.”

A HEETMA map of both leaks repaired in recent years and current known leaks shows that one leak was fixed Sept. 8 in the area of 20 Buchanan Road. There are no other leaks identified nearby. The next closest leak on the map is on Jefferson Avenue.

“We want to work with the gas company and get these lines repaired, so the study going on to find these gas leaks is a good thing,” Dibble said. “And we need to hold the gas company’s feet to the fire and get them all repaired.”

The LORAX Task Force — a group of tree advocates advancing an arbor-friendly agenda — is hammering out details for a tree ordinance due to be presented to the City Council in the coming months, Dibble said. He also plans to file something with the councilors that would “require a higher level of service to get these leaks repaired and lines replaced,” he said.

“Boston has a good ordinance now that’s on the books, but we don’t have one here in Salem,” Dibble said. “And I think we need one.”